1. Field of the Invention
The present invention relates to a method and a system for monitoring tyres fitted to vehicles, during use thereof. This monitoring is performed by processing data detected on the tyre so as to obtain behavioural indices which can be associated with the working life of said tyre.
2. Description of the Related Art
The patent U.S. Pat. No. 5,737,215 describes a method and an apparatus for comparing with each other vehicles forming part of a fleet, whereby an apparatus compares various characteristics of the vehicles in a fleet so as to produce a signal indicating a deviation from a predefined reference value. This signal is designed to determine which components of the vehicles are not functioning or do not comply with the normal operating specifications. A predefined database is used as a device for comparing the parameters representing said vehicle characteristics. Said parameters consist of three types: values detected by sensors, values calculated by means of functions and values indicating a deviation from values detected by sensors.
The patent U.S. Pat. No. 4,773,011 describes a method for monitoring, selecting and evaluating vehicle tyres. In particular, this patent describes a method for monitoring the state of tyres fitted to vehicles in order to manage in an optimum manner tyres used by fleets of vehicles, for example lorries. A computer analyses information relating to the tyres of each vehicle in the fleet in order to check for example the wear thereof. In this patent, this information consists of the inflation pressure and the depth of the grooves in the tread band. The data may be processed in a microcomputer, one of which is present in each vehicle, or processed in a central computer. Among the various functions the system also calculates the cost per kilometer of the tyres.
U.S. Pat. No. 4,862,486 describes a revolution counter associated with a tyre. In particular, the patent describes a piezoelectric sensor associated with the tyre, able to emit an electric signal during each revolution of the tyre when the latter makes contact with the ground. This signal is processed and sent to a counter which determines the number of rotations performed by the tyre. The sensor is designed to determine the number of kilometers travelled by the tyre during its working life.
A tyre basically consists of a torus-shaped carcass generally comprising at least one reinforcing ply provided with textile or metallic cords lying in the radial planes, i.e. containing the axis of rotation of the tyre. The ends of the carcass ply are preferably folded back, axially outwards from the inside, around two metal annular cores—usually called “bead wires” —which form the reinforcement for the beads, namely the radially internal ends of said tyre. The beads allow assembly of the tyre on a corresponding mounting rim.
A tread band is positioned on the peripheral rim of said carcass and has, formed in it, a tread pattern by means of which the tyre makes contact with the ground. The tread band has a thickness of predetermined value and is defined between an outer surface, intended to make contact with the ground, and an inner surface, preferably lined with a thin fixing layer (“liner”) designed to ensure the necessary adhesion between the material of the tread band and that of a belt assembly. The abovementioned belt assembly is an annular reinforcing structure which is circumferentially unextendable and arranged between the carcass and the tread band. Generally the belt structure comprises at least two radially superimposed layers of rubberized fabric provided with metal reinforcing cords. In each layer said cords are arranged parallel to each other and intersecting with respect to the cords of the adjacent layers; preferably, the cords in said layers are also arranged symmetrically inclined with respect to the equatorial plane of the tyre. Preferably, the belt structure also comprises a further, radially external, layer of cords oriented circumferentially with respect to the tyre, usually known as 0° cords.
A tyre of this type is described in the patent application EP 613 794 in the name of the same Applicants.
Tyres for heavy vehicles, such as road haulage vehicles, vehicles used for quarry and construction work, coaches for transporting persons, etc., constitute a significant proportion of the vehicle management costs, with the result that it is currently the practice to replace the totally worn tread band with a new tread band by means of a process which is generally called “remoulding”. Preferably, this process envisages the removal of the remainder of a worn tread band and, after a visual analysis of the tyre carcass in order to check its condition, the deposition of a new tread band. If the new tread band consists of unprocessed material, the carcass thus lined is inserted into a vulcanization mould where moulding of the tread band and vulcanization of the new band on the old carcass is performed. Alternatively, tread bands which are pre-moulded with a suitable tread pattern and pre-vulcanized may be used and in this case are bonded to the old carcass using suitable adhesives.
In the case of the abovementioned vehicles the new tyres are generally mounted on the front steering axles, whereas the remould tyres are mounted on the driving or driven rear axles and the trailer axles.
For example, in the case of a heavy vehicle comprising an engine cab with a front steering axle, a first rear driving axle, a second rear idle axle and a trailer, the tyres are arranged as follows:                new tyres are mounted on the front steering axle;        tyres which have been remoulded once are mounted on the rear axles;        tyres which have been remoulded more than once are mounted on the trailer axles.        
On the basis of this type of use of the tyres, the costs per kilometer of the tyre and the probable residual working life may vary considerably from tyre to tyre: monitoring this situation constitutes a problem for a vehicle fleet manager which becomes increasingly complex with an increase in the number of vehicles in the fleet and which requires, among other things, the management of a suitable stock of spare tyres.